1. Field of the Invention
This invention relates to a resin composition which has good compatibility of individual components contained therein and is substantially free of any flow anomaly, and also to a multilayered structure which exhibits a good appearance and has good impact resistance, delamination resistance, and gas barrier properties.
2. Description of the Prior Art
Multilayered plastic packaging materials are known wherein a layer of a thermoplastic resin, particularly a polyolefin resin (hereinafter referred to simply as PO), having good moistureproofing and mechanical characteristics and a layer of a saponified product of an ethylene-vinyl ester copolymer (hereinafter referred to simply as EVOH) having good oxygen barrier properties are laminated through an adhesive resin. Such packaging materials have wide utility in various fields such as of foods, cosmetics, medicines and chemicals, toiletries and the like as containers having good oxygen barrier properties in the form of bottles, cups, pouches and the like.
When the multilayered plastic containers are fabricated, it is inevitable that burrs be undesirably produced owing to the pinch-off for blow molding and regrinds (scraps) such as of waste plastics after punching be left for cup molding. Accordingly, the re-use of these inevitable scraps has been accepted as being necessary from the standpoint of costs and resource saving. In order to effectively re-use the regrinds, there have been proposed several methods including a method wherein the regrinds are mixed in the thermoplastic resin layer primarily made of a polyolefin (Japanese Patent Publication No. Sho 59-29409), and a method wherein a regrind layer is provided between the thermoplastic layer such as of a polyolefin and the EVOH layer (Japanese Patent Laid-open No. Sho 59-101338). However, where regrind resins containing thermoplastic resins, especially polyolefin resins, and the EVOH are subjected to co-melt extrusion molding, the EVOH tends to deteriorate. During the course of the blend melt extrusion, black deposits ("charred resin") may be formed in the inside of the extruder, or gel-like matters ("lip stain") may be deposited such as on the dielip during the extrusion. This eventually leads to the troubles such as the formation of foreign matters resulting from non-uniform phase separation, flow anomalies, a lowering in appearance of the resultant molded container, the generation of offensive odor from the decomposed resins, lowerings of mechanical characteristics such as impact resistance, and the like. Thus, the extrusion molding of such a composition as mentioned above has been substantially impossible to perform, or can, if ever, be carried out only for a short time in most cases. On the other hand, where the blend of a polyolefin and EVOH and EVOH are subjected to co-extrusion molding, wavy patterns are formed on the surfaces of molded articles, along with delamination (intralayer and interlaminar separations) occurring in the articles.
Japanese Patent Laid-open No. Sho 49-57086 (corresponding to U.S. Pat. No. 3,931,449) has proposed the blends of thermoplastic resins having carbonyl groups at the main chain or side chains thereof (e.g., ionomers, maleic anhydride-grafted polypropylene, ethylene-maleic anhydride copolymer and the like) with low density polyethylene and EVOH in order to improve working properties thereof. Japanese Patent Laid-open No. Hei 3-72539 (corresponding to European Patent 401,666) has proposed the blends of an EVOH having a high content of ethylene and polyolefins modified through grafting of unsaturated carboxylic acids thereto, with polyolefins and EVOH so as to improve the appearance of molded articles obtained therefrom. Further, Japanese Patent Laid-open No. Hei 5-98084 has proposed the blends of unsaturated carboxylic acid-modified polyolefins with polyolefins and EVOH in order to improve a resistance to environmental stress-cracking.
However, as will become apparent from Comparative Examples 5 to 7 and 12 to 14, the compositions comprising ionomers, maleic anhydride-grafted polypropylene and ethylene-maleic anhydride copolymer, respectively, are not satisfactory with respect to the impact resistance and the intralayer separation strength.
Moreover, it is stated in Japanese Patent Laid-open No. Sho 61-111346 (U.S. Pat. No. 4,619,969) that the impact resistance is improved by blending copolymers of ethylene, unsaturated dicarboxylic acid anhydrides and unsaturated esters having from 4 to 12 carbon atoms.
In Japanese Patent Laid-open No. Hei 2-16163, it is set out that blending of inorganic fillers and copolymers of ethylene, acrylic esters and maleic acid derivatives with thermoplastic resins such as EVOH can suppress whitening on mechanical rubbing. However, the above-mentioned U.S. Pat. No. 4,619,969 and the Japanese Patent Laid-open No. Hei 2-16163 do not set forth the use of the ethylene-maleic anhydride-acrylic ester copolymer as a compatible agent for EVOH and polyolefins.